In resent years, much attention has been given to the option of using non-contact equipment for supporting, gripping or conveying products in manufacturing processes. In particular, such non-contact equipment has a unique appeal for high-tech industry where the production is highly susceptible to direct contact. It is especially important in the semiconductors industry, in the manufacturing phase of silicon wafers, Flat Panel Displays (FPD) and Printed Circle Boards (PCB), as well as computer's hard-discs, compact discs (CD), DVD, liquid crystal display (LCD) and similar products. Non-contact equipment can beneficially be applied also in the manufacturing phase of optical equipment and in the printing world, mainly in wide format printing when apart from papers, printing is performed on various types of “hard” materials.
By using non-contact equipment, many problems that are associated with the manufacturing phase may be solved and directly enhance the production yield. Without derogating the generality, some of the advantages in using non-contact systems includes, inter alia:    (a) Eliminating or greatly reducing mechanical damages—including, for example, impact, press, but, most importantly, any friction that may be involved. Friction is inherently eliminated in non-contact systems.    (b) Eliminating or greatly reducing in-contact contamination—a very important feature for semiconductors production lines of silicon wafers and FPDs.    (c) Eliminating or greatly reducing electrostatic discharge (ESD). Critical ESD problems may be founds in the semiconductors production lines of FPD and silicon wafers.    (d) Eliminating or greatly reducing in-contact local deformation of objects due to particles that are trapped on the contact surface, between the product and the in-contact equipment. Such problems may occur when a wafer is gripped by an electrostatic or vacuum chuck during a sequential lithography process in the semiconductors industry.    (e) Non-flatness of local nature, found in in-contact equipment, is inherently averaged when using non-contact equipment.Additional benefits of using non-contact equipments can be obtained:    (f) Conveying of products by moving only the product thus avoiding the need to move also the holding-table that may be of much heavier weight than the product itself, a situation that is typically found in the FPD market and semiconductors industry as well as in the printing world.    (g) Conveying the product accurately where accuracy can be provided only at a small distinct area or along a narrow line where the process is executed continuously of step-by-step during the travel of the product. It is relevant in steppers that are widely in use the semiconductors industry with planar (X,Y) wafer motion is applied, when rotating the wafer during inspection, or when linear motion in one direction is applied in the manufacturing line of FPD.    (h) To flatten with no contact, by pure moments enforcing, objects that are not flat, in order to provide accurate gripping. It is important for PCB & FPD makers as well as in the semiconductors industry where both regular or thin wafers have to be flatten prior to many processes. It is also important in the printing world when media other than paper is used, including direct digital writing on different media, and printing-plate for off-set printing and press. In most of these examples, optics or optical imaging is involved where the focal distance must be very accurate.
Commonly, such systems comprise a flat platform having one or more active-surfaces. Each of the active-surfaces, that are in most cases flat, is equipped with a plurality of pressure ports for providing pressurized air aimed at generating an air-cushion. An air-cushion is developed when a surface, that is flat in most cases, is placed over the active surface at a close range. Air-cushion support can be preloaded by the object weight, by pressure dual-side configuration or preloaded by vacuum. In case of light weight, as in many cases of the products mentioned above, high performance air-cushion support, in many cases, adopts the pressure or vacuum preloading approaches.
Currently used non-contact supporting and conveying systems that are based on air-cushions offer limited performance in many aspects. These limited performance aspects are mainly related to the relatively high mass flow or energy consumption associated with these systems, and to the accuracy performance that is directly related to the aero-mechanic stiffness of the air-cushion. The non-contact supporting and conveying equipment of the present invention that implements various types of air-cushions, employing a plurality of flow-restrictors that are functioning as a “fluidic return springs”, and provide effective high-performance air-cushion support at much lower mass flow consumption with respect to conventional non-contact equipment. In particular, when using non-contact platforms where the active-area is much larger than the confronting surface of the supported object and most of the platform's active area is not cover, the use of flow restrictors provides an efficient and cost-effective non-contact platform in terms of mass flow consumption. With respect to the present invention, a flow restrictor is individually installed in each conduit of the pressure ports of the non-contact platform active-area. By active area is meant, throughout the present specification the area of the support surface where injecting ports are distributed. It is preferred, for the purposes of the present invention, to use self-adaptive segmented orifice (SASO) nozzles as the preferred flow-restrictors, so as to effectively produce the fluidic return spring effect.
PCT/IL00/00500, published as WO 01/14752, entitled APPARATUS FOR INDUCING FORCES BY FLUID INJECTION, described the SASO nozzle and its uses in non-contact supporting systems. It is a purpose of the present invention to provide, in preferred embodiment of the present invention, a novel high-performance non-contact supporting and conveying platforms based on air-cushion technology that employs the SASO nozzle as a fluidic return spring and that is capable of limiting the flow of air through these nozzles.
The self adaptive segmented orifice (SASO) flow control device comprising a fluid conduit, having an inlet and outlet, provided with two opposite sets of fins mounted on the inside of the conduit, each two fins of same set and a portion of the conduit internal wall between them defining a cavity and the fin of the opposite set positioned opposite said cavity, so that when fluid flows through the conduit substantially stationary vortices are formed in the cavities said vortex existing at least temporarily during the flow thus forming an aerodynamic blockage allowing a central core-flow between the vortices and the tips of the opposite set of fins and suppressing the flow in a one-dimensional manner, thus limiting the mass flow rate and maintaining a substantial pressure drop within the conduit. It exhibits the following characteristics of the SASO nozzle:    (a) A fluidic return spring effect is established when pressurized air is supplied at the inlet to the SASO-nozzle and the outlet is partially blocked by an objects but not closed completely, allowing air flow out of the outlet, in such a way that a potion of the supply pressure is dropped inside each of the SASO-nozzles and the remaining pressure is introduced to the air cushion, that is developed in the narrow gap between the “active surface” of that platform having the SASO-nozzle outlets and the surface of the object, thus force is applied on the object to elevate it. The pressure introduced to the air cushion is increased as the gap is decreased and is decreased as the gap is increased. If, for example, the object is supported by an air-cushion, this pressure establishes a force that balances the object's weight. The object is floating over the non-contact platform active-surface at a self-adaptive manner where, with respect to this example, the air-cushion gap is self-defined to such a levitation distance that the total forces up-wise that act on the floating object are equal to the gravity force. The fluidic return spring behavior is obtained when trying to change that balanced situation: when trying to close the gap, the pressure at the air-cushion is increased and pushes the object up to the balanced air-cushion gap, and when trying to open the gap, the pressure at the air-cushion is decreased and the gravity force pulls the object down to the balanced air-cushion gap. This simple example is given to clarify the functionality of the fluidic return spring, but in general it can be applied in various ways as will be discussed hereinafter.    (b) An aerodynamic blockage mechanism is obtained when the SASO-nozzle outlet is not closed. In fact, a SASO-nozzle has laterally large physical scales to prevent mechanical blockage by contaminating particles, and when it is totally covered (as the flow stops, the aerodynamic blockage dissipates), it introduces pressure or vacuum at the platform active surface with no losses. But, when the SASO-nozzle outlet is not closed and a through-flow exists, it has a dynamic behavior of a small orifice that is controlled by the aerodynamic blockage mechanism. This behavior is significantly important as the mass flow rate is dramatically reduced when the non-contact platform supporting or conveying a smaller in size object and a large portion of it's active surface is not covered.
The SASO-nozzle is a flow-control device that has a self-adaptive nature, based purely on aero-dynamic mechanism, with no-moving parts or any means of controls. As it has laterally large physical scales, it is not sensitive to contamination blockage. When using a plurality of SASO-nozzles to feed a well functioning air-cushion, it has a local behavior that provides homogeneous air-cushion.